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Unformatted text preview: 2/23/12 Initial setup
1. Open Wolfram CDF Player and
RandomWalkCircles 5 simulation.
Click “Enable Dynamics” button.
2. Adjust the stimulation window by
expanding the inner square to fill
the screen as shown here.
3. Open your Google account and
use the link emailed to you to open
4. Play with the simulation according
to the instructions on the handout. Diffusion in Cells
Diffusion works fine across membranes, organelles, and most cells In general, no need to evolve special mechanisms for facilitating
the movement of most molecules via diffusion over short distances.
(Exception: the challenge of membrane permeability) Multicellular eukaryotes: The limits of diffusion
1) To visualize how the random movement of molecules can result in their net
movement down a concentration gradient;
2) To gain a quantitative perspective of how the diffusion works as a physical
3) To analyze how the limits of diffusion have affected the evolution and
functioning of large multicellular organisms in eukaryotic lineages.
In-class activities: computer simulations for understanding the fundamental principles
governing diffusion as a physical process
Group homework: several problems for illustrating the role of diffusion in biological
systems. Homework assignment will be posted on the class website. Due next Friday. Transport systems in animals ventilatory, circulatory, digestive, and
excretory systems F Fig. 44.11
• Convection of medium (air)
• Diffusion of O2 and CO2
across alveolar membranes Circulation
• Convection of medium (blood)
• Diffusion of gases, food molecules,
waste molecules across capillary
membranes 1 2/23/12 Simulation #1 - Tuning
everyone’s computer Noise – 0.012
Time - 20 sec
outside or on
circle 4 -> no reset
Otherwise – reset
noise and rerun
simulation Simulation #2 - to obtain a qualitative sense for how diffusion works
Settings - Noise at 0.03 Particles at 100
Run the simulation and watch what happens.
Simulations #3-#5 – to obtain a quantitative perspective of the
relationship between concentration gradient (i.e., a concentration
difference over a distance) and diffusion rate (Fick’s First Law)
#3 Noise at reset level from simulation #1 Particle number – 50 Run time – 20 s
Data collection – count the number of particles on or outside circle 4
Enter the data in the table
Recenter all particles, repeat twice, and calculate mean particle number
#4 Same, but set particle number – 100
#5 Same, but particle number – 150
Fill out the row for your group data on the Google docs spreadsheet called
“BSCI207Diffusion_DataSpr12” which is accessed via your Google account. Simulation #6 – to determine the quantitative relationship between
time and distance traveled for individual molecules (Time-to-Diffuse
equation, also called the Einstein-Smoluchowski relation)
Settings – Noise at the reset level from simulation #1 Particles at 5
Run the simulation for 20 s intervals (do not recenter!)
Measure the distance of each particle from the 0 circle to the closest circle,
which corresponds to the distance traveled 2 ...
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This note was uploaded on 04/05/2012 for the course BSCI 207 taught by Professor Higgins during the Spring '08 term at Maryland.
- Spring '08